A burner is typically monitored with the aid of an electrode placed at the periphery of the flame. The electrode is coupled to an electric circuit which is unable to conduct electric current until the circuit is connected between electrode and burner or flame pipe as a result of ionization at the flame periphery. Alternatively, there is used a UV-detector for detecting the ultra violet radiation that occurs in the presence of combustion.
Ionization detection requires the placement of an electrode in the edge of the flame, whereas UV-detection requires the ability to capture said UV-radiation.
A problem occurs with ionizing detection in the case of so-called high speed burners. In the case of high speed burners, a fuel mixture flows from the burner head at a high velocity, meaning that the length and the position of the flame will vary with the velocity of the outflowing fuel mixture. The position of the flame therefore requires an electrode whose length is greater than the electrode of a conventional burner and which hangs freely or, in the best of cases, can be supported with the aid of a ceramic outer pipe. There must be no metallic contact with the burner.
The problem is further accentuated by the desire to use a detection electrode to ignite the flame, by applying a high voltage through the electrode in order to generate a spark between its forward part and the burner upstream of the inrushing fuel/air mixture. The use of a high voltage means that the electrode must be enclosed by a ceramic pipe in order to isolate the electrode from the burner, meaning that the cross-sectional surface area of the electrode will be other than negligible in respect of the fuel-mixture delivery channel of the burner.
A typical ignition electrode that is dimensioned to ensure sufficient shape stability and oxidation length of life will, together with an insulating ceramic, reduce considerably the space available for conducting fuel and combustion air/premix air.
In addition to a high speed burner producing a variable flame form, the position of the electrode becomes more critical when power is increased. The best ionization is obtained at the edge of the flame. An electrode which is placed along the longitudinal axis of the burner will either function poorly or not at all.
Eccentric positioning of the electrode will result in disturbance of the flame symmetry.
It has been observed that in the case of UV-detection a UV-sensor viewing angle that deviates axially is highly sensitive to the position of the flame.
These problems are resolved by means of the present invention, the object of which is to provide a construction which is less pretentious with regard to the cross-sectional area of the burner than traditional present day solutions, while maintaining mechanical stability and oxidation life length.